1. Field of the Invention
The present invention relates to photodetector binning. More specifically, the present invention relates to a method and apparatus for providing flexible photodetector binning.
2. Related Art
In the field of optoelectronics, it is often desirable to increase the sensitivity of photodetectors. A common technique utilized in the art to achieve increased photosensitivity is pixel binning. Binning is desirable in applications such as wavefront sensing, digital zoom functions, and other applications where low light level imaging is required. The binning procedure increases the effective pixel size of the photodetector by combining the outputs of a plurality of pixels in a given region.
Binning techniques have been used extensively with charged coupled devices (CCDs) to increase the amount of signal produced by the device prior to on-chip amplification. However, visible active pixel sensors (APSs) and infrared focal plane arrays (FPAs) typically do not include binning capabilities due to voltage and current mode readout limitations of such detectors. Some APS and FPA circuits incorporate binning at the column level by using charge output from the pixels, and other circuits incorporate binning on the integration capacitor node. These methods are often undesirable because they occur after non-negligible noise sources are introduced by the readout circuit, thereby limiting improvements in the signal-to-noise ratio (SNR) of the device. Binning within the pixel provides the advantage of increasing a device's readout rate, but requires the addition of in-pixel switches to connect integration nodes together. This results in increased manufacturing complexity and costs, as well as limiting the ability to minimize pixel area and increasing the potential for crosstalk between pixels when the binning function is not activated.
Another limitation of existing binning techniques common to CCDs, APSs, and FPAs is that such techniques are limited to binning in fixed geometries determined by the implementation of CCD, APS, or FPA circuits. Previous binning techniques used in CCDs, APS, and FPAs achieve a sum of a number of pixels that form the subset of a larger pixel array, but cannot bin across partial pixel areas.
Accordingly, what would be desirable, but has not heretofore been provided, is a method and apparatus for providing flexible photodetector binning, wherein pixel binning can be performed across any desired number of pixels, or portions thereof, in any desired pattern or geometry.